Somatosensory System Flashcards
What are the 3 types of somatosensory systems
Cutaneous (skin) sensation
Visceral (internal organs)
Proprioception (identity of limbs)
Which receptors in somatosensory system convert stimuli eg light into AP
Sensory receptors
What is a stimuli converted to in first step of sensory transduction
Receptor / graded potential
What happens if receptor/ grades potential reaches threshold due to large stimulus
AP can be fired
In AP initiation what suggests large stimulus
AP frequency
On the skin, what are the 2 layers called
Top epidermis and bottom dermis
Where are most receptors in skin found
In dermis (superficial)
What are the 4 skin receptors which are superficial
Merkels disk
Meissner corpuscle
Hair follicle receptor
Free nerve (no receptor)
What are the 2 types or deep receptors
Pacinian corpuscle
Ruffini’s corpuscle
What are the 3 nerve fibres connected to skin receptors
AB - large and myelinated (fastest)
A delta - small and myelinated
C - small and unmyelinated (slowest)
What is a receptive field
Area which a stimulus activates receptors and the nerve fibres
Which 2 receptors have small receptive fields
Meissner corpuscle and merkels disk
Which skin receptor detects stroking in a direction (large RF)
Ruffinis
What are slow adaptation receptors
Receptors which have a receptor potential and therefore fire AP all the way through a stimulus
What are fast adapting receptors
Receptors which have receptor potential / AP firing at start and end of stimulus not during
What are fast adapting receptors useful for
Identifying change Eg the slipping of an object
What on a pacinian corpuscle allows it to have a rapid adaptation
It’s capsule (bends during a stimulus, then pushes back at end of stimulus = rapid adaptation)
What are bare nerve endings for (superficial skin endings)
Detection of warm or cold temperatures
Which nerve is attached to bare nerve endings in skin to detect warm temp
C fibre (small and unmyelinated)
Which nerve ending defects cold in skin
A delta (small and myelinated)
Which receptors detect pain/ noxious stimuli
Nociceptors
What are 4 types of nociceptors
Mechanical (crushing pricking pain)
Thermal pain
First pain (stabbing)
Second pain (burning)
What detects sharp sensation (first pain)
A delta nerve endings
Which nerve detects second pain (burning)
C fibre
Which 2 receptors are ones with slow adaptation
Merkels disk and Ruffinis
Which nerve is attached to all but temp/ bare nerve endings
AB (large and myelinated)
What are the 2 pathways transmitting cutaneous signals eg from AB to the brain
Dorsal column pathway DC
Spinothalmic tract STT pathway
What do fibres synapse with / cross over in the grey matter for the STT ventral pathway
Neurones from grey matter to the STT then to brain
Where does crossing over (decussation) of fibres happen in the DC pathway after moving from Dorsal columns to brain
Medulla (dorsal column nuclei)
Where is the first synapse in DC pathway unlike STT in the grey matter
Medulla (dorsal column nuclei)
What happens in decussation of DC fibres
They move to opposite side of brain
Where is the second synapse between in the DC pathway
Thalamus and somatosensory cortex
What does decussation mean for info on different sides of body
Left body info goes to right brain cortex
Right body info goes to left brain cortex
What info is in DC pathway
recognition of objects/ fine touch and also detection of movement on skin surface
Which system allows edges of objects to be detected in dc pathway
Lateral inhibition
Explain steps of lateral inhibition
Receptor potential highest in nerve below the stimulus more than others
More NT released
Larger stimulation of secondary neurones due to more NT
Secondary neurones from other areas are pre synaptically inhibited (IPSP)
Only 1 tertiary neurone is stimulated large , others there is no AP
What inhibits lateral neurones
Fibres from other receptive fields
Where does neurone from grey matter carrying into to in STT
To ventral side then to thalamus then to somatosensory cortex
Which area of somatosensory cortex is STT into in
Post central gyrus
Where is the post central gyrus
Behind the central sulcus (middle parting)
How is info laid out in the post central gyrus
Laid out depending on body part eg head on right and leg info on left
What is post central gyrus mapping called
Somatotopic representation
